We have identified a mouse with the lysosomal storage disease, mucopolysaccharidosis type VII (MPS VII). There is little if any beta- glucuronidase activity present in these mice because of a very low level of beta-glucuronidase mRNA. The exact nature of the mutation is unknown, but it maps to the beta-glucuronidase locus, Gus, on Chromosome 5. This is the first mouse with MPS VII and it is an important discovery for several reasons. The Gus locus, which contains the beta- glucuronidase structural gene as well as three regulatory elements, has been the subject of intense study at the genetic and biochemical levels. Recently, both the human and mouse structural genes have been cloned. We plan to clone the gene from mutant mice and determine the nature of the genetic defect at the DNA sequence level to help identify regulatory elements required for normal expression of this enzyme. In addition, study of the pathophysiology of the disease in mice will be beneficial in explaining the variable clinical manifestations of the disease in humans, and a detailed analysis of the cellular pathology using light and electron microscopes will indicate which specific cell types in each tissue are affected by the accumulation of glycosaminoglycans. Finally, murine MPS VII is an excellent system in which to explore the feasibility of gene therapy in human patients who have lysosomal storage diseases. The specific aims of this proposal are to: 1. Characterize the clinical course and histopathology of murine MPS VII. 2. Determine the nature of the genetic defect at the DNA sequence level by cloning the mutant Gus locus and comparing it to the normal locus. 3. Generate transgenic mice with normal human and mouse genes to identify the DNA sequences required for normal gene expression and then determine whether this expression is sufficient to completely cure the mutant mice. 4. Transplant bone marrow stem cells of syngeneic normal mice into mutant mice to determine which histopathological changes and disease symptoms are alleviated by this form of therapy. 5. Use retroviral vectors constructed by Drs. Eli Gilboa and John Wolfe containing human and mouse genes to infect bone marrow stem cells from mutant mice in vitro and then determine whether transplantation of these cells back into mutant mice improves the host's clinical condition and lifespan.